Render is duplicating random frames when loaded into 3D tracker
Most likely the video is recorded using a LongGOP format and not an intraframe codec.
http://tiliam.com/Blog/2015/07/06/effective-use-long-gop-video-codecs/
What that means is that every frame does not contain the full information for the picture, but only records the changes from a reference (I) frame. Blender has a hard time dealing with that format.
Try exporting the video as an image sequence or a video format with intraframe encoding, so that every frame is available to blender for tracking.
Another common error is using video files recorded on some phones and screen recording software that encode using a variable frame rate. Blender cannot deal with such files correctly, they need to be converted to a stable frame rate (or an image sequence) in an external app, before importing into blender.